I’ve not heard it but you might take a look at the Cayin C9, which @antdroid reviewed here. I don’t know if the Cayin N8 DAP would be suitable, e.g. re. power, but FWIW, Cayin seems to be the most prominent manufacturer of portable gear that uses tubes.
Cayin also makes DAPs, or at least it used to make them - as with the N6ii DAP - that have replaceable modules, e.g. the one with an R2R DAC. I’ve not used any Cayin products but I’ve seen people praise them on the forums.